1. Field of the Invention
The present invention relates to a process that provides an intuitive and user-friendly means for the modeling and rendering of computer-displayed free-form solid objects. A host of approaches have been taken over the past several decades in the depiction of three-dimensional solids on two-dimensional computer screens. Commonly, mathematically defined solid primitives are manipulated andr combined to create the desired illusion. For example, a sphere could be placed atop a construction of cylinders corresponding to a torso, arms, and legs to approximate a crude human shape. For another example, a tetrahedron and two spheres could be attached to the surface of a larger ovoid ball to represent a crude nose, two eyes, and a head. These examples highlight the fact that the spatial characteristics of most anatomical and other natural objects do not have simple mathematical analogues. Unfortunately, computer visualization systems are largely dependant upon such analogues for the representation of any object or surface. This has precluded the professional sculptor (and in many cases, the professional designer), who is generally not highly skilled in the arcana of computer visualization mechanics, from contributing his artistic talents to the rendering of free-form solid computer images. Conversely, mathematically adept computer specialists, who are not generally skilled in the visual fine arts, have had the burden of providing such images.
2. Description of the Prior Art
Various tools have been developed in an attempt to circumvent this shortcoming. Some tools begin with solid primitives and then allow free-form manipulation via onscreen menu commands sometimes along with the additional use of a digitizing puck, light pen, mouse, or other related input device. Some examples of such devices are described in L. Williams, "3D Paint," Computer Graphics, 24 (2):225-233, March, 1990; Sederberg, T. W. and S. R. Parry, "Free-Form Deformation of Solid Geometric Models," Computer Graphics, 20(4):151-160, August, 1986; S. Coquillart, "Extended Free-Form Deformation: A sculpting tool for 3D Geometric Modeling," Computer Graphics, 24(4):187-196, August 1990; and Pentland, A., et. al, "The ThingWorld Modeling System: Virtual Sculpting by Modal Forces," Computer Graphics, 24(2):143-146, March 1990.
Other approaches involve the use of a three-dimensional input device, corresponding to a "virtual" tool, which can remove, add, or smooth "material" from an initial "block" of "clay". This development is described in Galyean, T. A. and J. F. Hughes, "Sculpting: An Interactive Volumetric Modeling Technique," Computer Graphics, 25(4):267-274, July, 1991. Although this device is perhaps the most intuitively appealing of the current approaches, it presently lacks true tactile feedback. Furthermore, due to its adoption of a voxel-based, as opposed to a polygon-based system, this device is computationally demanding. So much so, in fact, that it requires powerful workstations presently beyond the affordability of most artisans.
No matter what the approach, in order to render a solid object, a computer graphic display system must at a minimum have geometric information specific to the object. A secondary requirement is information on surface textures, hidden surfaces, light sources, perspective, shading, and other attributes. All of these features can augment the appearance of three-dimensionality of an object, but they all necessarily rely on a priori knowledge of the location of the object, with reference to a world coordinate system, and the specific volume in space that it occupies.